Many combustion devices produce particulate emissions. For example, diesel engines are increasing in popularity in many kinds of vehicles. In the meantime, environmental regulations relative to particulate emissions are becoming more stringent. Thus, there is need for minimizing emissions from diesel engines and other particulate emitting mechanisms.
PM emissions contribute to the fine particle burden in the atmosphere. and the EPA has established a light-duty vehicle PM emission standard of 0.08 g/mile and has promulgated a regulation to limit the amount of particular matter with a diameter of 2.5 microns or less (such as the newer 0.1 micron standard being considered). To meet these standards, engine manufacturers have developed low-emission engines. Technological improvements may have reduced mass emissions, but it has been said the newer engines meeting the 1991 emissions limit requirements had dramatically increased numbers and volumes of very small nuclei mode particles when compared to similar engines meeting 1988 emissions limit requirements. These observations suggest that not only accumulation mode size particles, but also nuclei size particles may pose future emission problems.
Particulate matter (PM) sensors are used in internal combustion engines to determine combustion characteristics, particularly with respect to soot that results from incomplete combustion.